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PAVING & DECKING

Decking Rotting

Decking rot may affect only surface boards or extend into joists and posts, where it becomes a structural safety issue.

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Make trip and fall hazards safe first

Loose slabs, rotten decking and slippery surfaces can cause serious injury. Stop using elevated or structurally soft decking until it has been assessed.

MOST LIKELY CAUSES

Start with movement, support and drainage

Persistent moisture Timber remains wet and cannot dry.
Poor ventilation Airflow beneath the deck is restricted.
Untreated cuts and end grain Water enters exposed timber.
Debris traps Leaves and soil hold moisture against boards and joists.
◫ Symptom variations Match the movement, cracking or surface condition. ⌄
  • Timber feels soft
  • Boards crumble at fixings
  • Dark patches persist
  • Mushroom growth appears
  • Deck flexes underfoot
✓ Quick checks Safe checks before lifting slabs or boards. ⌄
  1. Probe suspect timber gently.
  2. Inspect board ends and fixing points.
  3. Check joists and posts underneath.
  4. Look for trapped soil and leaves.
  5. Stop using areas that flex or feel soft.
Important: Fix the support, drainage or structural cause before replacing surface materials.
1 Step 1 — Find the full extent Make the smallest safe correction and retest. ⌄

Do not assume only the visible board is affected.

2 Step 2 — Remove rotten timber Make the smallest safe correction and retest. ⌄

Cut back to sound material.

3 Step 3 — Replace and protect Make the smallest safe correction and retest. ⌄

Use suitable treated timber and improve drainage and ventilation.

⌁ Why the problem happens How support, water and movement affect paving and decking. ⌄

Rot develops when timber moisture remains high for long periods, especially at joints and concealed surfaces.

⌘ Advanced checks Further diagnosis for persistent outdoor surface faults. ⌄
  1. Measure moisture content.
  2. Inspect ledger connections.
  3. Check post bases.
  4. Assess joist hangers and fixings.
  5. Review drainage beneath the deck.
◇ Tools and information needed Useful items for accurate checks. ⌄
  • Moisture meter
  • Screwdriver or probe
  • Pry bar
  • Saw
  • Safety gloves
▣ Parts or materials that may help Common paving and decking materials linked to this fault. ⌄
  • Treated deck boards
  • Joists
  • Posts
  • Joist tape
  • Exterior fixings
! When to call a professional Conditions that should end basic DIY diagnosis. ⌄
  • Joists or posts are affected.
  • The deck is elevated.
  • Guarding or stairs are rotten.
  • Large areas flex.
  • Structural connections are uncertain.
? Frequently asked questions Common paving and decking questions. ⌄

Can rotten wood be filled?

Only cosmetic surface defects. Structurally soft timber should be replaced.

Why does rot start around screws?

Water collects around fixings and exposed end grain.

Should all boards be replaced?

Only damaged boards, unless widespread age or hidden rot makes full renewal sensible.